Repetition coding in a satellite-based communications system

ABSTRACT

A satellite communications system comprises a transmitter, a satellite transponder and a receiver. The transmitter transmits an uplink multi-level modulated signal (hierarchical modulation or layered modulation) to the satellite transponder, which broadcasts the multi-level modulated signal downlink to one, or more, receivers. The transmitter includes a repetition coder for repetition coding at least one level, e.g., a lower level, of the multi-level modulated signal. In complementary fashion, the receiver includes a repetition decoder for use in decoding the at least one repetition coded level of the received multi-level modulated signal.

This application claims the benefit, under 35 U.S.C. § 365 ofInternational Application PCT/US04/013478, filed Apr. 30, 2004, whichwas published in accordance with PCT Article 21(2) on Dec. 2, 2004 inEnglish and which claims the benefit of U.S. provisional patentapplication No. 60/471,166 filed May 16, 2003.

BACKGROUND OF THE INVENTION

The present invention generally relates to communications systems and,more particularly, to satellite-based communications systems.

As described in U.S. Pat. No. 5,966,412 issued Oct. 12, 1999 toRamaswamy, hierarchical modulation can be used in a satellite system asa way to continue to support existing legacy receivers yet also providea growth path for offering new services. In other words, a hierarchicalmodulation based satellite system permits additional features, orservices, to be added to the system without requiring existing users tobuy new satellite receivers. In a hierarchical modulation basedcommunications system, at least two signals, e.g., an upper layer (UL)signal and a lower layer (LL) signal, are added together to generate asynchronously modulated satellite signal for transmission. In thecontext of a satellite-based communications system that providesbackward compatibility, the LL signal provides additional services,while the UL signal provides the legacy services, i.e., the UL signalis, in effect, the same signal that was transmitted before—thus, thesatellite transmission signal can continue to evolve with no impact tousers with legacy receivers. As such, a user who already has a legacyreceiver can continue to use the legacy receiver until such time thatthe user decides to upgrade to a receiver, or box, that can recover theLL signal to provide the additional services.

In a similar vein, a layered modulation based communication system canalso be used to provide an approach that is backward compatible. In alayered modulation based system at least two signals are modulated(again, e.g., a UL signal (legacy services) and an LL signal (additionalservices)) onto the same carrier (possibly asynchronously with eachother). Transmission of the UL signal and the LL signal occur separatelyvia two transponders and the front end of a layered modulation receivercombines them before recovery of the data transported therein.

SUMMARY OF THE INVENTION

Whether a hierarchical based modulation or a layered based modulation,we have observed that receiver performance in the presence of noise canbe further improved in a multi-level transmission scheme. In particular,and in accordance with the principles of the invention, a transmitterincludes a repetition coder for repeating at least a portion of at leastone signal of a multi-level modulation scheme to provide a repetitioncoded signal, and a modulator for providing a multi-level transmissionsignal, which includes the repetition coded signal.

In an embodiment of the invention, a satellite communications systemcomprises a transmitter, a satellite transponder and a receiver. Thetransmitter transmits an uplink multi-level modulated signal(hierarchical modulation or layered modulation) to the satellitetransponder, which broadcasts the multi-level modulated signal downlinkto one, or more, receivers. The transmitter includes a repetition coderfor repetition coding at least one level, e.g., a lower level, of themulti-level modulated signal. In complementary fashion, the receiverincludes a repetition decoder for use in decoding the at least onerepetition coded level of the received multi-level modulated signal.

In another embodiment of the invention, the receiver is a unifiedreceiver, which operates in any one of a number of demodulation modesfor demodulating a received multi-level signal, wherein at least two ofthe number of demodulation modes are a hierarchical demodulation modeand a layered demodulation mode. The unified receiver includes arepetition decoder for use in decoding at least one repetition codedlevel of the received multi-level modulated signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustrative satellite communications system embodyingthe principles of the invention;

FIG. 2 shows an illustrative block diagram of a transmission paththrough satellite 15 of FIG. 1;

FIG. 3 shows an illustrative hierarchical modulation embodiment inaccordance with the principles of the invention for use in transmitter 5of FIG. 1;

FIG. 4 illustrates repetition coding in accordance with the principlesof the invention;

FIG. 5 shows illustrative symbol constellations for use in the upperlayer and the lower layer;

FIG. 6 shows another illustrative hierarchical modulation embodiment inaccordance with the principles of the invention for use in transmitter 5of FIG. 1;

FIG. 7 shows an illustrative resulting signal point constellation for amulti-level signal;

FIG. 8 shows an illustrative layered modulation embodiment in accordancewith the principles of the invention for use in transmitter 5 of FIG. 1;

FIG. 9 shows an illustrative block diagram of a satellite transmissionpath in the context of a layered modulation based system;

FIG. 10 shows an illustrative block diagram of a receiver in accordancewith the principles of the invention;

FIG. 11 shows an illustrative block diagram of unifieddemodulator/decoder 320 of FIG. 10 in accordance with the principles ofthe invention;

FIGS. 12-16 show various blocks diagrams of different portions ofunified demodulator/decoder 320 in accordance with the principles of theinvention;

FIG. 17 shows an illustrative signal space;

FIG. 18 shows an illustrative log-likelihood look-up table in accordancewith the principles of the invention;

FIG. 19 shows an illustrative symbol constellation;

FIGS. 20 and 21 illustrate log-likelihood calculations;

FIG. 22 shows an embodiment of metric grouping element 595 of FIG. 11;

FIG. 23 shows another variation of H-L mux 395 of FIG. 11;

FIGS. 24-25 show other illustrative embodiments of a unifieddemodulator/decoder in accordance with the principles of the invention;and

FIG. 26 shows an illustrative flow chart in accordance with theprinciples of the invention.

FIG. 27 shows another illustrative embodiment of a layered modulationreceiver in accordance with the principles of the invention;

FIG. 28 shows another illustrative embodiment of a hierarchicalmodulation receiver with simultaneous decoding in accordance with theprinciples of the invention; and

FIG. 29 shows another illustrative embodiment of a hierarchicalmodulation receiver with sequential decoding in accordance with theprinciples of the invention.

DETAILED DESCRIPTION

Other than the inventive concept, the elements shown in the figures arewell known and will not be described in detail. Also, familiarity withsatellite-based systems is assumed and is not described in detailherein. For example, other than the inventive concept, satellitetransponders, downlink signals, symbol constellations, a radio-frequency(rf) front-end, or receiver section, such as a low noise blockdownconverter, formatting and encoding methods (such as Moving PictureExpert Group (MPEG)-2 Systems Standard (ISO/IEC 13818-1)) for generatingtransport bit streams and decoding methods such as log-likelihoodratios, soft-input-soft-output (SISO) decoders, Viterbi decoders arewell-known and not described herein. In addition, the inventive conceptmay be implemented using conventional programming techniques, which, assuch, will not be described herein. Finally, like-numbers on the figuresrepresent similar elements.

An illustrative communications system 50 in accordance with theprinciples of the invention is shown in FIG. 1. Communications system 50includes transmitter 5, satellite channel 25, receiver 30 and television(TV) 35. Although described in more detail below, the following is abrief overview of communications system 50. Transmitter 5 receives anumber of data streams as represented by signals 4-1 through 4-K and, inaccordance with the principles of the invention, provides a multi-levelmodulated signal 6 to satellite transmission channel 25 such that atleast one level of the multi-modulated signal 6 is repetition coded(described further below). Illustratively, these data streams representcontrol signaling, content (e.g., video), etc., of a satellite TV systemand may be independent of each other or related to each other, or acombination thereof. The multi-level modulated signal 6 representseither a hierarchical modulation based signal or a layered modulationbased signal having K layers, where K≧2. It should be noted that thewords “layer” and “level” are used interchangeably herein. Satellitechannel 25 includes a transmitting antenna 10, a satellite 15 and areceiving antenna 20. Transmitting antenna 10 (representative of aground transmitting station) provides multi-level modulated signal 6 asuplink signal 11 to satellite 15. Referring briefly to FIG. 2, anillustrative block diagram of the transmission path through satellite 15for a signal is shown. Satellite 15 includes an input filter 155, atraveling wave tube amplifier (TWTA) 165 and an output filter 175. Theuplink signal 11 is first filtered by input filter 155, then amplifiedfor retransmission by TWTA 165. The output signal from TWTA 165 is thenfiltered by output filter 175 to provide downlink signal 16 (which istypically at a different frequency than the uplink signal). As such,satellite 15 provides for retransmission of the received uplink signalvia downlink signal 16 to a broadcast area. This broadcast areatypically covers a predefined geographical region, e.g., a portion ofthe continental United States. Turning back to FIG. 1, downlink signal16 is received by receiving antenna 20, which provides a received signal29 to receiver 30, which demodulates and decodes received signal 29 inaccordance with the principles of the invention to provide, e.g.,content to TV 35, via signal 31, for viewing thereon. It should be notedthat although not described herein, transmitter 5 may further predistortthe signal before transmission to compensate for non-linearities in thechannel.

As noted above, in the context of this description multi-level modulatedsignal 6 represents either a hierarchical modulation based signal or alayered modulation based signal. In the case of the former, anillustrative block diagram for transmitter 5 in accordance with theprinciples of the invention is shown in FIG. 3; while in the latter casean illustrative block diagram for transmitter 5 in accordance with theprinciples of the invention is shown in FIG. 7. In the remainder of thisdescription it is illustratively assumed that there are two datastreams, i.e., K=2. It should be noted that the invention is not limitedto K=2 and, in fact, a particular data stream such as signal 4-1 mayalready represent an aggregation of other data streams (not shown).

As noted earlier, we have observed that receiver performance in thepresence of noise can be further improved in a multi-level transmissionscheme. In particular, and in accordance with the principles of theinvention, a transmitter includes a repetition coder for repeating atleast a portion of at least one signal of a multi-level modulationscheme to provide a repetition coded signal, and a modulator forproviding a multi-level transmission signal, which includes therepetition coded signal. It should be noted that performing arepetition-coding scheme on at least one level, e.g., the lower layer,effectively trades off data rate for signal-to-noise ratio (SNR) on thatlayer. In other words, although the effective data rate of the lowerlayer is reduced, the use of repetition-coding allows the receiver torecover data from the lower layer in lower SNR environments. Thus, andas described further below, transmitter 5 repetition codes at least aportion of at least one signal level of a multi-level signal and thentransmits the multi-level signal, including the repetition coded portionthereof.

Turning first to FIG. 3, an illustrative hierarchical modulationtransmitter for use in transmitter 5 is shown. Hierarchical modulationis simply described as a synchronous modulation system where a lowerlayer signal is synchronously embedded into an upper layer signal so asto create a higher order modulation alphabet.

In FIG. 3, the hierarchical modulation transmitter comprises UL encoder105, UL modulator 115, LL encoder 110, repetition coder 170, LLmodulator 120, multipliers (or amplifiers) 125 and 30, combiner (oradder) 135 and up converter 140. The upper layer (UL) path isrepresented by UL encoder 105, UL modulator 115 and amplifier 125; whilethe lower layer (LL) path is represented by LL encoder 110, repetitioncoder 170, LL modulator 120 and amplifier 130. As used herein, the term“UL signal” refers to any signal in the UL path and will be apparentfrom the context. For example, in the context of FIG. 3, this is one ormore of the signals 4-1, 106 and 116. Similarly, the term “LL signal”refers to any signal in the LL path. Again, in the context of FIG. 3,this is one of more of the signals 4-2, 111, 171 and 121. Further, eachof the encoders implement known error detection/correction codes (e.g.,convolutional or trellis codes; concatenated forward error correction(FEC) scheme, where a rate ½, ⅔, ⅘ or 6/7 convolutional code is used asan inner code, and a Reed Solomon code is used as an outer code; LDPCcodes (low density parity check codes); etc.). For example, typically ULencoder 105 uses a convolutional code or a short block code; while LLencoder 110 uses a turbo code or LDPC code. For the purposes of thisdescription it is assumed that LL encoder 110 uses an LDPC code. Inaddition, a convolutional interleaver (not shown) may also be used.

As can be observed from FIG. 3, signal 4-2 is applied to LL encoder 110,which provides an encoded signal 111. Likewise, signal 4-1 is applied toan UL encoder 105, which provides an encoded signal 106 to modulator115. Encoded signal 106 represents N bits per symbol interval T; whileencoded signal 111 represents M bits every JT symbol intervals, where Nmay, or may not, equal M and J>1. Repetition coder 170 furtherrepetition codes encoded signal 111 by receiving the M bits of dataevery J symbol intervals and providing the M bits of data every symbolinterval to modulator 120. In other words, repetition coder 170 repeats,or duplicates, the M bits of data across the J symbol intervals. In thiscontext, the grouping of the M bits across the J symbol intervals or thegrouping of the associated J symbols, define a symbol group orrepetition symbol. This is illustrated in FIG. 4 for J=2. LL encoder 110provides M1 bits to repetition coder 170 in 2T time interval 41.Repetition coder 170 provides the M1 bits to modulator 120 (operating atthe symbol rate 1/T) in time interval 42 and, again, in time interval43. Modulators 115 and 120 modulate the respective signals appliedthereto to provide modulated signals 116 and 121, respectively. Itshould be noted that since there are two modulators, 115 and 120, themodulation can be different in the UL path and the LL path. Again, forthe purposes of this description it is assumed that the number of ULencoded data bits is two, i.e., N=2, and that UL modulator 115 generatesa modulated signal 116 that lies in one of four quadrants of a signalspace. That is, UL modulator 115 maps two encoded data bits to one offour signal points. Similarly, the number of LL encoded data bits isalso assumed to be two, i.e., M=2, and LL modulator 120 also generates amodulated signal 121 that lies in one of four quadrants of the signalspace. An illustrative symbol constellation 89 for use in both the ULand the LL is shown in FIG. 5. In this example, each repetition symbol44 of the LL is mapped from J identical M-bit groups from repetitioncoder 170 into symbols from symbol constellation 89. It should be notedthat signal space 89 is merely illustrative and that symbolconstellations of other sizes and shapes can be used. Turning briefly toFIG. 6, another illustrative embodiment for implementing hierarchicalmodulation in transmitter 5 is shown. FIG. 6 is similar to FIG. 3 exceptthat hierarchical modulator 180 performs the mapping of the lower layerand upper layer bits into the combined signal space. For example, theupper layer may be a QPSK (quadrature phase-shift keying) signal space,while the lower layer is a BPSK (binary phase-shift keying) signalspace; combining the two could result, e.g., in a non-uniform 8-PSKsignal space.

Returning to FIG. 3, the output signals from UL modulator 115 and LLmodulator 120 are further adjusted in amplitude by a predefined UL gainand a predefined LL gain via amplifiers 125 and 130, respectively. Itshould be noted that the gains of the lower and upper layer signalsdetermine the ultimate placement of the points in the signal space. Forexample, the UL gain may be set to unity, i.e., 1, while the LL gain maybe set to 0.5. The UL signal and the LL signal are then combined viacombiner, or adder, 135, which provides combined signal 136. Thus, themodulator of FIG. 3, e.g., the amplifiers 125 and 130, along withcombiner 135, effectively further rearranges and partitions the signalspace such that the UL signal specifies one of the four quadrants of thesignal space; while the LL signal specifies one of a number ofsubquadrants of a particular quadrant of the signal space as illustratedin FIG. 7 by signal space 79.

In effect, the resulting signal space 79, also referred to herein as thecombined signal space 79, comprises 16 symbols, each symbol located at aparticular signal point in the signal space and associated with aparticular four bits. For example, symbol 83 is associated with the fourbit sequence “01 01”. The lower two bit portion 81 is associated withthe UL and specifies a quadrant of signal space 79; while the upper twobit portion 82 is associated with the LL and specifies a subquadrant ofthe quadrant specified by two bit portion 81. It should be noted thatsince the UL signal identifies the quadrant, the LL signal effectivelylooks like noise on the UL signal. Returning to FIG. 3, the combinedsignal 136 is applied to up converter 140, which provides multi-levelmodulated signal 6 at the appropriate transmission frequency.

From this example, it can be observed from FIG. 7 that, in effect, eachsymbol in a transmitted sequence may be different from a followingsymbol since only the upper two bit portion associated with the LLsignal is repeated over the J symbol intervals of a symbol group. Assuch, the two resulting symbols (not shown) from signal space 79representing the M1 bits in time intervals 42 and 43 of FIG. 4 alsocomprise repetition symbol 44.

Turning now to FIG. 8, an illustrative block diagram of a layeredmodulator in accordance with the principles of the invention for use intransmitter 5 of FIG. 1 is shown. Here, transmitter 5 comprises twoseparate transmitter paths. The upper layer path includes UL encoder105, UL modulator 115 and up converter 240. The lower layer pathincludes LL encoder 110, repetition coder 170, LL modulator 120 and upconverter 245. Signal 4-1 is encoded by UL encoder 105 to provideencoded signal 106 representing N bits every symbol interval, T, andsignal 4-2 is encoded by LL encoder 110 to provide encoded signal 111representing M bits every J symbol intervals. Again, each of theencoders implement known error detection/correction codes and M may, ormay not, be equal to N. The UL encoded signal 106 is then modulated byUL modulator 115 to provide UL modulated signal 116, which is thenupconverted to the appropriate frequency band to provide UL signal 6-1.However, LL encoded signal 111 is first applied to repetition coder 170which repeats the M bits over J symbol intervals, as described above.The resulting repetition-coded signal 171 is applied to LL modulator120, which provides LL modulated signal 121, which is then upconvertedby up converter 245 to provide LL signal 6-2. It should be observed fromFIG. 8 that transmitter 5 transmits two signals, i.e., multi-levelmodulated signal 6 comprises UL signal 6-1 and repetition-coded LLsignal 6-2. Typically, LL signal 6-2 is transmitted at a lower powerlevel than UL signal 6-1. This effectively lowers the SNR for the LLpath. However, and in accordance with a feature of the invention, theuse of repetition coding on the LL path improves the performance ofreceiver 30 of FIG. 1 for lower SNRs at the expense of a reduced datarate over the LL path.

As such, and referring now to FIG. 9, for a layered modulation basedsystem uplink signal 11 represents two uplink signals—UL uplink signal11-1 and LL uplink signal 11-2; while downlink signal 16 represents twodownlink signals: LL downlink signal 16-2 and UL downlink signal 16-1.In this example, satellite 15 of FIG. 1 may be a single satellite withtwo different transponders (one for the UL signal and the other for theLL signal) or two different satellites. Whether one satellite or two, asshown in FIG. 9 there are, in effect, two satellite transmission paths.The UL satellite path includes UL input filter 255, UL TWTA 265 and ULoutput filter 275, which provides UL downlink signal 16-1; while the LLsatellite path includes LL input filter 260, LL TWTA 270 and LL outputfilter 280, which provides LL downlink signal 16-2. Each of the elementsof FIG. 9 function in a similar fashion to the respective elements shownin FIG. 2 and described earlier.

As noted above, after reception of the downlink signal 16 by receivingantenna 20, receiver 30 demodulates and decodes received signal 29 toprovide, e.g., content to TV 35 for viewing thereon. An illustrativeportion of receiver 30 in accordance with the principles of theinvention is shown in FIG. 10. Receiver 30 includes front end filter305, analog-to-digital converter 310 and unified demodulator/decoder320. The latter, in accordance with the principles of the invention,includes a repetition decoder. Front end filter 305 down-converts andfilters received signal 29 to provide a near base-band signal to A/D310, which samples the down converted signal to convert the signal tothe digital domain and provide a sequence of samples 311 (also referredto as multi-level signal 311) to unified demodulator/decoder 320. Thelatter has a number of demodulation modes, where at least two of thedemodulation modes represent a hierarchical demodulation mode and alayered demodulation mode. The selection of a particular demodulationmode is provided by demodulation mode signal 389, which isillustratively set a priori. Demodulation mode signal 389 can be set inany one of a number of ways, e.g., a jumper setting, configurationinformation (not shown) of receiver 30 that may be viewable, e.g., on TVset 35, and settable, e.g., via a remote control (not shown), or fromdata transmitted on an out-of-band or an in-band signaling channel. Ifset in the hierarchical demodulation mode, unified demodulator/decoder320 performs hierarchical demodulation of multi-level signal 311 andprovides a number of output signals, 321-1 to 321-K, representative ofdata conveyed by multi-level signal 311 on the K layers. Data from oneor more of these output signals are provided to TV set 35 via signal 31.(In this regard, receiver 30 may additionally process the data beforeapplication to TV set 35 and/or directly provide the data to TV set 35.)In the following example the number of levels is two, i.e., K=2, but theinventive concept is not so limited. For example, in the hierarchicaldemodulation mode, unified demodulator/decoder 320 provides UL signal321-1 and LL signal 321-2. The former ideally represents what wastransmitted on the upper layer, i.e., signal 4-1 of FIG. 3; while thelatter ideally represents what was transmitted on the lower layer, i.e.,signal 4-2 of FIG. 3. Similarly, if set in the layered demodulationmode, unified demodulator/decoder 320 performs layered demodulation ofmulti-level signal 311 to provide UL signal 321-1 and LL signal 321-2,which ideally represents signals 4-1 and 4-2 of FIG. 8.

Turning now to FIG. 11, an illustrative architecture for unifieddemodulator/decoder 320 is shown. Unified demodulator/decoder 320comprises UL demodulator 330, delay/equalizer element 345, UL decoder335, UL remodulator/reencoder 350, combiner 375, LL demodulator 390, H-Lmultiplexer (H-L mux) 395 (also referred to herein as H-L selector 395),metric grouping element 595 and LL decoder 340. Multi-level signal 311is applied to UL demodulator 330, which demodulates this signal andprovides therefrom a UL carrier signal 332, a resampled multi-levelsignal 316 and a demodulated UL signal as represented by demodulated ULsignal point stream 333. Referring now to FIG. 12, an illustrative blockdiagram of UL demodulator 330 is shown. UL demodulator 330 includesdigital resampler 415, matched filter 420, derotator 425, timingrecovery element 435 and carrier recovery element 440. Multi-levelsignal 311 is applied to digital resampler 415, which resamplesmulti-level signal 311 using UL timing signal 436, which is provided bytiming recovery element 435, to provide resampled multi-level signal316. Resampled multi-level signal 316 is applied to matched filter 420and is also provided to delay/equalizer element 345 (described below).Matched filter 420 is a band-pass filter for filtering resampledmulti-level signal 316 about the UL carrier frequency to provide afiltered signal to both derotator 425 and the above-mentioned timingrecovery element 435, which generates therefrom UL timing signal 436.Derotator 425 derotates, i.e., removes the carrier from the filteredsignal to provide a demodulated UL signal point stream 333. Carrierrecover element 440 uses the demodulated UL signal point stream 333 torecover therefrom UL carrier signal 332, which is applied to derotator425 and to UL remodulator/reencoder 350 (described below).

Referring back to FIG. 11, UL decoder 335 acts in a complementaryfashion to corresponding UL encoder 105 of transmitter 5 and decodes thedemodulated UL signal point stream 333 to provide UL signal 321-1. Asnoted above, UL signal 321-1 represents the data conveyed on the upperlayer, e.g., as represented by signal 4-1 of FIGS. 3 and 8. It should beobserved that UL decoder 321-1 recovers the data conveyed in the UL by,in effect, treating the LL signal as noise on the UL signal. In otherwords, UL decoder 335 operates as if UL signal 333 represents symbolsselected from signal space 89 of FIG. 5.

UL signal 321-1 is also applied to remodulator/reencoder 350, which,responsive to UL carrier signal 332, locally reconstructs the ULmodulated signal. In particular, remodulator/reencoder 350 reencodes andthen remodulates UL signal 321-1 to provide UL modulated signal 351 to anegative input terminal of combiner 375. Referring briefly to FIG. 13, ablock diagram of an illustrative remodulator/reencoder 350 is shown.Remodulator/reencoder 350 includes rotate phase delay element 445,encoder 470, rerotator 465 and pulse shaping element 460. Encoder 470reencodes and remaps to symbols UL signal 321-1 to provide an encodedsignal 471 to rerotator 465, which re-rotates encoded signal 471 by adelayed version of the locally generated UL carrier frequency, asdetermined by the upper layer carrier recovery element 440. The outputsignal from rerotator 465 is applied to pulse shaping element 460, whichfurther shapes the reconstructed signal to provide UL modulated signal351.

Turning back to FIG. 11, combiner 375 subtracts UL modulated signal 351from a delayed and equalized version (signal 346) of resampledmulti-level signal 316 to provide a signal representative of just thereceived LL modulated signal, i.e., LL modulated signal 376, which isalso used to update taps (not shown) of the equalizer of delay/equalizerelement 345.

The two input signals to the combiner 375 are at the same sampling rate,which is typically an integer multiple of the upper layer symbol rate.An illustrative block diagram of delay/equalizer element 345 is shown inFIG. 14. Delay/equalizer element 345 includes signal delay element 450and equalizer 455. Signal delay element 450 compensates for the delay inthe signal processing path through UL demodulator 330, decoder 335 andremodulator/reencoder 350; while equalizer 455 attempts to remove lineardistortions, such as tilts on the signal path in the tuner, such thatcombiner 375, in effect, cancels as much of the UL signal as possiblefrom the resampled multi-level signal 316 to provide a clean ILmodulated signal 376. In other words, equalization is performed tooptimally match the UL component of resampled multi-level signal 316 tolocally reconstructed UL modulated signal 351 so as to optimally removethe UL signal before demodulating and decoding the LL signal.

Returning again to FIG. 11, LL modulated signal 376 is then applied toLL demodulator 390, which recovers therefrom a demodulated LL signal asrepresented by demodulated LL signal point stream 391. An illustrativeblock diagram of LL demodulator 390 is shown in FIG. 15. LL demodulator390 includes digital resampler 515, matched filter 520, timing recoveryelement 535, derotator 525, and carrier recovery element 540. LLmodulated signal 376 is applied to digital resampler 515, whichresamples LL modulated signal 376 using LL timing signal 536 to bringthe LL signal to the initial LL processing rate, which is typically, aninteger multiple of the lower layer symbol rate. Digital resampler 515works in conjunction with timing recovery element 535. Resampled LLmodulated signal 516 is applied to matched filter 520, which is aband-pass filter for filtering and shaping resampled LL modulated signal516 about the LL carrier frequency to provide a filtered signal to bothderotator 525 and the above-mentioned timing recovery element 535, whichgenerates therefrom LL timing signal 536. Derotator 525 derotates thefiltered signal to provide a demodulated LL signal point stream 391,which is also applied to carrier recover element 540. The latter usesthe demodulated LL signal point stream 391 to provide a recovered LLcarrier signal to derotator 525.

Returning once again to FIG. 11, H-L mux 395 receives demodulated ULsignal point stream 333 and demodulated LL signal point stream 391. H-Lmux 395 selects either UL signal point stream 333 or LL signal pointstream 391 for processing and subsequent application to metric groupingelement 595 as a function of demodulation mode signal 389. Ifdemodulation mode signal 389 indicates layered demodulation, then H-Lmux 395 selects LL signal point stream 391 for processing. However, ifdemodulation select signal 389 indicates hierarchical demodulation, thenH-L mux 395 selects UL signal point stream 333 for processing.

Attention should now be directed to FIG. 16, which shows an illustrativeblock diagram of H-L mux 395. The latter comprises multiplexer (mux) 565and log-likelihood ratio (LLR) look-up table (LUT) 570. The inputsignals to H-L mux 395 are received signal point values (either from theUL or the LL) and the output signals of H-L mux 395 are soft valuesrepresenting the probability that certain bits were received. Inparticular, Mux 565 selects either UL signal point stream 333 or LLsignal point stream 391 as a function of demodulation mode signal 389,as described above, and provides the selected signal as received signal566. As such, received signal 566 is a stream of received signal points,each received signal point having an in-phase (I_(REC)) component (572)and a quadrature (Q_(REC)) component (571) in a signal space. This isfurther illustrated in FIG. 17 for a received signal point z, where:z=I _(rec) +jQ _(rec).   (1)

The I_(REC) and Q_(REC) components of each received signal point areapplied to LLR LUT 570. The latter stores a LUT 599 of precomputed LLRvalues as illustrated in FIG. 18. In particular, each row of LUT 599 isassociated with a particular I component value (an I row value), whileeach column of LUT 599 is associated with a particular Q component value(a Q column value). LUT 599 has L rows and J columns. LIR LUT 570quantizes the I_(REC) and Q_(REC) component values of a received signalpoint of received signal 566 to form an input address, which is used asan index into LUT 599 for selecting therefrom a respective precomputedLLR. Each symbol interval, T, the selected LLR is provided via signal396. For example, if the I_(REC) component value of signal 566 isquantized to the first row and the Q_(REC) component value of signal 566is quantized to the first column, then LLR 598 would be selected andprovided via signal 396 of FIG. 16 to metric grouping element 595 ofFIG. 11.

Other than the inventive concept, and as known in the art, for a givenbit-to-symbol mapping M(b_(i)), where M are the target symbols and bi=0,1, . . . B-1, are the bits to be mapped where B is the number of bits ineach symbol (e.g., B may be two bits for QPSK, three bits for 8-PSK,etc.), the log-likelihood ratio function for the ith bit of a B bitvalue is:LLR(i, z)=log [(prob(b _(i)=1|z))/(prob (b _(i)=0|z))];   (2)where b_(i) is the ith bit and z is the received signal point in thesignal space. The notation “prob (bi=1|z)” represents the probabilitythat the ith bit is a “1” given that the signal point z was received.Similarly, the notation “prob (bi=0|z)” represents the probability thatthe ith bit is a “0” given that the signal point z was received.

For a two-dimensional signal space, the probabilities within equation(2) are assumed to be based upon additive Gaussian white noise (AWGN)having a probability density function (PDF) of:

$\begin{matrix}{{{prob}(n)} = {\frac{\exp( \frac{- {n}^{2}}{2\sigma^{2}} )}{2\pi\;\sigma^{2}}.}} & (3)\end{matrix}$Therefore, the LLR for a given bit and received signal point are definedas:

$\begin{matrix}{{{LLR}( {i,z} )} = {{\log\lbrack \frac{\sum\limits_{M_{{{bit}\mspace{11mu} 1} = 1}}{\exp( \frac{- {{z - M}}^{2}}{2\sigma^{2}} )}}{\sum\limits_{M_{{{bit}\mspace{11mu} 1} = 0}}{\exp( \frac{- {{z - M}}^{2}}{2\sigma^{2}} )}} \rbrack}.}} & (4)\end{matrix}$It can be observed from equation (4) that the LLR for a given receivedsignal point z is a function of z, the target symbols M, and the rmsnoise level σ. An LLR is also one example of a “soft metric.”

A pictorial illustration of the calculation of an LLR ratio is shown inFIGS. 19 and 20. FIG. 19 shows an illustrative LL symbol constellation.For simplicity a 4 symbol QPSK (quadrature phase shift keyed)constellation is shown, however, it should noted that other sizes andshapes of symbol constellations could also have been used, e.g., 3 bitsfor 8-PSK, 4 bits for 16-QAM, a hierarchical 16-QAM, etc. As can beobserved from FIG. 19, there are four symbols in the signal space 89,each symbol associated with a particular two bit mapping [b1, b0].Turning now to FIG. 20, a received signal point z is shown in relationto the symbols of signal space 89. It can be observed from FIG. 20 thatthe received signal point z is located at different distances d_(i) fromeach of the symbols of signal space 89. For example, the received signalpoint z is located a distance d₄ from the symbol associated with the twobit mapping “01.” As such, the LLRe(b0) is:ln [(probability b0 is one)/(probability b0 is zero)]; or   (5A)ln [(probability (symbol 01 or 11))/(probability (symbol 00 or 10))]; or  (5B)ln [{exp(−d ₄ ²/(2σ²))+exp(−d ₃ ²/2σ²))}/{exp(−d ₂ ²/(2σ²))+exp(−d ₁²/(2σ²))}].   (5C)while the LLR(b1) is:ln [(probability b1 is one)/(probability b1 is zero)]; or   (6A)ln [(probability (symbol 10 or 11))/(probability(symbol 00 or 01))]; or  (6B)ln [{exp(−d ₁ ²/(2σ²))+exp(−d ₃ ²/(2σ²))}/{exp(−d ₂ ²/(2σ²))+exp(−d ₄²/(2σ²))}].   (6C)

Returning to FIG. 16, it can be observed that LLR LUT 570 (i.e., LUT599) is initialized to either a set of hierarchical LLR values 573 orlayered LLR values 574 depending on the respective mode of receiver 30.For example, the layered TTR values are calculated a priori with respectto a LL symbol constellation such as illustrated in FIGS. 5, 19 and 20;while the hierarchical LLR values are calculated a priori with respectto the combined symbol constellation such as the one illustrated in FIG.7 and shown again in FIG. 21. In other words, the hierarchical LLRs forthe LL are determined—not with respect to the LL signal space (e.g.,signal space 89 of FIG. 5)—but with respect to the combined signal space(e.g., signal space 79 of FIG. 7). For every received signal point z, adistance between each symbol of signal space 79 and the received signalpoint z is determined and used in calculating an LLR. For simplicity,only some of these distances, d_(i), are shown in FIG. 21. Thehierarchical LLR values 573 and the layered LLR values 574 can be formedin any number of ways. For example, receiver 30 may perform thecalculations by using, e.g., a training signal, provided by transmitter5 either during start-up, or re-initialization, of communicationsbetween the two endpoints (transmitter 5 and receiver 30). As known inthe art, a training signal is a predefined signal, e.g., a predefinedsymbol sequence that is known a priori to the receiver. A predefined“handshaking” sequence may further be defined, where the endpointsexchange signaling before communicating data therebetween.Alternatively, the calculations may be performed remotely, e.g., at thelocation of transmitter 5 and sent to receiver 30 via an in-band orout-of-band signaling channel (this could even be via a dial-up facility(wired and/or wireless) (not shown)). Or, the LLR values can becalculated based on expected signal conditions, and stored in thereceiver at the time of manufacture.

Referring back to FIG. 11, in accordance with the principles of theinvention metric grouping element 595 receives the sequence of LLRs (thesoft input data), via signal 396, and provides therefrom repetitiondecoded signal 596. Mustratively, metric grouping element 595 performsthe functions of aligning the repetition symbols with symbols andproviding an LLR output value for each repetition symbol, as describedbelow and illustrated in FIG. 22. For illustrative purposes, metricgrouping element 595 is shown for the case J=2, although J can be anynumber greater than one. Metric grouping element 595 comprises phaseaveragers 630 and 635, absolute value elements 640 and 645, low-passfilters 650 and 655, comparator 660 and multiplexer 670.

The first function performed by metric group element 595 is, in effect,alignment of the received signal point sequence in the LL to arepetition symbol period. As noted earlier, each transmitted LLrepetition symbol includes J symbols, where J>1. In this regard, metricgrouping element 595 processes the sequence of LLRs (represented bysignal 396) to group those associated with the same repetition symbolperiod. This alignment, or grouping, can be performed in any number ofways. Here, Phase 1 Averager 630 takes LLR values 396 as input, andprovides output LLR values averaged over each repetition symbol(LLR0+LLR1), (LLR2+LLR3) . . . as signal 631, while Phase 2 Averager 635takes LLR values 396 as input, and provides output LLR values averagedover each repetition symbol with another alignment (LLR1+LLR2),(LLR3+LLR4) . . . as signal 636. Signal 631 is further processed byabsolute value element 640 to provide absolute values signal 641, whichis further processed by low-pass filter (LPF) 650 to provide filteredsignal 651. Signal 636 is further processed by absolute value element645 to provide absolute values signal 646, which is further processed bylow-pass filter (LPF) 655 to provide filtered signal 656. Comparator 660receives the low-pass filtered signals 651 and 656 and creates selectsignal 661, which is one if signal 651 is greater than signal 656,indicating that Phase 1 is a better alignment, or zero otherwise,indicating that Phase 2 is a better alignment. The select signal 661 isapplied to multiplexer (MUX) 670, which then passes the averagedrepetition symbol LLR values according to the determined betteralignment: that is, it selects signal 631, corresponding to Phase 1, ifthe select signal 661 is a one or signal 636, if the select signal 661is a zero, to provide LLR output 596. Thus, metric grouping element 595passes the summed LLRs associated with the best alignment phase as thecombination metric and provides this average LLR every repetition symbolperiod to LL decoder 340 as repetition decoded signal 596. Thus, groupmetric element 595, in effect, removes the duplicated data from the LLsignal.

LL decoder 340 receives the sequence of average LLRs (the soft inputdata), via signal 596, and provides therefrom LL signal 321-2. LLdecoder 340 operates in a complementary fashion to that of LL encoder10. It should also be noted that LL decoder 340 may also be asoft-input-soft-output decoder, and provide soft output values, whichare then additionally processed (not shown) to form LL signal 321-2.

It can be observed from FIG. 11 that in a layered demodulation modereceiver 30 sequentially demodulates the received signal by firstrecovering the UL signal via UL demodulator 330 and decoder 335. Therecovered UL signal is then reencoded and remodulated for subtractionfrom the received signal to uncover the LL signal for demodulation by LLdemodulator 390. The resulting demodulated LL signal point stream 391 isthen processed to generate soft input data, e.g., LLRs, with respect tothe LL symbol constellation. In contrast, in a hierarchical demodulationmode, the UL signal point stream 333 is recovered, from which the LL,signal is then directly determined. This is referred to herein as asimultaneous mode of decoding. In particular, the UL signal point stream333 is processed to generate soft input data, e.g., LLRs, to recovertherefrom the LL data.

Other variations of H-L mux 395 are possible. For example, FIG. 23 showsan illustration where two separate look-up tables (555 and 560) arelocated in front of mux 565, which selects the appropriate signal(either signal 556 or 561) in accordance with demodulation mode signal389.

Another embodiment in accordance with the principles of the invention isshown in FIG. 24. Illustratively, in this embodiment a unifieddemodulator/decoder 320′ sequentially decodes the received signal whenin the hierarchical mode of operation. For sequential decoding of ahierarchical modulation based signal, the receiver first decodes the ULsignal and then decodes the LL signal. As can be observed from FIG. 24,unified demodulator/decoder 320′ is similar to unifieddemodulator/decoder 320 of FIG. 11 except for the addition of combiner,or adder 380, delay element 355 and H-L mux 395′. Delay element 355compensates for the processing delay of UL decoder 335, encoder 470,etc. Illustratively, adder 380 receives as input signals the delayeddemodulated UL signal point stream 333′ and signal 471, which isavailable from UL remodulator/reencoder 350 as shown in FIG. 13.Combiner 380 subtracts the encoded signal 471 from delayed demodulatedUL signal point stream 333′ to provide an LL signal point stream 381 toan input of H-L mux 395′. As before, H-L mux 395′ selects the appliedsignals, here, either LL signal point stream 381 or the demodulated LLsignal point stream 391 as a function of the selected demodulation mode.

A block diagram of H-L mux 395′ is shown in FIG. 25. In this example,H-L mux 395′ includes mux 565 and LLR calculator 580. Mux 565 selectsbetween LL signal point stream 381 or the demodulated LL signal pointstream 391 as a function of demodulation mode signal 389 to providereceived signal point stream 566. The latter is applied to a soft datagenerator, such as represented by LLR calculator 580, which provides LLRdata 396 to group metric element 595, as described above.

Attention should now be directed to FIG. 26, for use in receiver 30 ofFIG. 1. In step 605, receiver 30 selects a one of a number ofdemodulation modes. Illustratively, there are at least two demodulationmodes: hierarchical demodulation and layered demodulation. As notedabove, this selection can be performed by, e.g., a jumper setting, aconfiguration screen (not shown) of receiver 30, or from datatransmitted on an out-of-band or an in-band signaling channel. In step610, receiver 30 receives a multi-level signal. In step 615, receiver 30determines the demodulation process to perform as a function of theselected demodulation mode. If the demodulation mode is hierarchical,then receiver 30 performs hierarchical demodulation of the receivedmulti-level signal in step 620. On the other hand, if the mode ofdemodulation is layered, then receiver 30 performs layered demodulationof the received multi-level signal in step 625. It should be noted thatselection of the demodulation mode (step 605) may be performed afterreceiving the multi-level signal (step 610).

Another embodiment of a receiver in accordance with the principles ofthe invention is shown in FIG. 27. Illustratively, in this embodimentreceiver 30 (not shown) only performs layered demodulation and includesdemodulator/decoder 720 for sequentially decoding a received signal. Ascan be observed from FIG. 27, demodulator/decoder 720 is similar tounified demodulator/decoder 320 of FIG. 11 except for the deletion of anumber of elements since hierarchical demodulation is not supported.

Illustratively, received signal point stream 391 is applied to LLRlookup table 570 which provides LLR values 396 to metric groupingelement 595. With respect to alignment, metric grouping element 595again aligns the received signal points by creating combined LLR valuesfor each of J possible alignments, and selects the best sequence ofcombined LLR values as that having, on average, the highest absolutevalue. As such, metric grouping element 595 then provides a repetitiondecoded signal 596 for application to LL decoder 340. In this context,LL decoder 340 receives LLR values.

Another embodiment of a receiver in accordance with the principles ofthe invention is shown in FIG. 28. Illustratively, in this embodimentreceiver 30 (not shown) only performs hierarchical demodulation andincludes demodulator/decoder 820 for simultaneously decoding a receivedsignal. As can be observed from FIG. 28, demodulator/decoder 820 issimilar to unified demodulator/decoder 320 of FIG. 11 except for thedeletion of a number of elements since layered demodulation is notsupported. As can be observed from FIG. 28, UL signal point stream 333is applied to LLR LUT 570, which has stored therein hierarchical LLRvalues 573, as described above. The resulting stream of LLRs (signal396) is applied to metric grouping element 595 as described earlier.

Another embodiment of a receiver in accordance with the principles ofthe invention is shown in FIG. 29. Illustratively, in this embodimentreceiver 30 (not shown) only performs hierarchical demodulation andincludes demodulator/decoder 920 for sequentially decoding a receivedsignal. As can be observed from FIG. 29, demodulator/decoder 920 issimilar to unified demodulator/decoder 320′ of FIGS. 24 and 25 exceptfor the deletion of a number of elements since layered demodulation isnot supported. Comments similar to those made with respect to the otherembodiments apply here, e.g., LL decoder 340 receives LLR values.

It should be noted that metric grouping element 595 can, in alternativeembodiments, operate upon symbol values, aligning and averaging them, inwhich case, for example, a LL decoder may first convert averaged symbolvalues into LLR values for subsequent decoding.

In accordance with a feature of the invention, the use of a repetitioncoder provides the ability to derive codes with additional designflexibility. For example, a rate ½ coder can be implemented by LLencoder 10 of FIG. 3. As known in the art, the nomenclature “rate ½”means that for every two bits transmitted, one bit is redundant (i.e.,provides for error protection/detection). In general form, a coder canbe stated to have a rate n/R, where n and R are greater than one andR>n. Further, in practice LL encoder 10 may be derived from an existingencoder design (proprietary or off-the shelf). Yet by adding repetitioncoding, transmitter 5 effectively implements a rate n/((R)(J))coder—without requiring a redesign in the encoder or correspondingdecoder—thus saving money and design time. It should also be noted thatrepetition coding as described herein can also be used in conjunctionwith puncturing and other techniques to derive classes of code ratesthat are usually not available otherwise.

As described above, and in accordance with the inventive concept,repetition coding is used on at least one level of a multi-level signal.Indeed, the inventive concept in effect creates a more robust LL channelthat allows recovery of data conveyed on the LL channel in lower SNRenvironments. Indeed, use of repetition coding on, e.g., the lowerlayer, improves receiver performance without increasing the power levelof the lower layer channel. As such, although described in the contextof repetition coding on a lower layer signal, the invention is not solimited and may be applied to any one or more layers of a multi-levelmodulated signal. Also, It should be noted that although described inthe context of a receiver coupled to a display as represented by TV 35,the inventive concept is not so limited. For example, receiver 30 may belocated further upstream in a distribution system, e.g., at a head-end,which then retransmits the content to other nodes and/or receivers of anetwork. Further, although hierarchical modulation and layeredmodulation were described in the context of providing communicationsystems that are backward compatible, this is not a requirement of theinventive concept. It should also be noted that groupings of componentsfor particular elements described and shown herein are merelyillustrative. For example, either or both UL decoder 335 and LL decoder340 may be external to element 320, which then is essentially ademodulator that provides at least a demodulated upper layer signal anda demodulated lower layer signal. Likewise, it should be noted thatalthough shown as a separate element, the functionality of repetitioncoder 170 can also be implemented in other elements of the figures.Consider for example, FIG. 3, the repetition coding function could beincluded within LL encoder 110 or LL modulator 120. Similar commentsapply to the other figures.

As such, the foregoing merely illustrates the principles of theinvention and it will thus be appreciated that those skilled in the artwill be able to devise numerous alternative arrangements which, althoughnot explicitly described herein, embody the principles of the inventionand are within its spirit and scope. For example, although illustratedin the context of separate functional elements, these functionalelements may be embodied on one or more integrated circuits (ICs).Similarly, although shown as separate elements, any or all of theelements may be implemented in a stored-programcontrolled processor,e.g., a digital signal processor (DSP) or microprocessor that executesassociated software, e.g., corresponding to one or more of the stepsshown in FIG. 26. Further, although shown as separate elements, theelements therein may be distributed in different units in anycombination thereof. For example, receiver 30 may be a part of TV 35. Itis therefore to be understood that numerous modifications may be made tothe illustrative embodiments and that other arrangements may be devisedwithout departing from the spirit and scope of the present invention asdefined by the appended claims.

1. A receiver comprising: a demodulator for demodulating a multi-levelreceived signal to provide K demodulated signals, where K>1; and arepetition decoder for removing duplicated data from at least one of theK demodulated signals; wherein the multi-level received signal is alayered modulated signal including at least an upper layer and a lowerlayer; and wherein the repetition decoder provides a repetition decodedsignal and wherein the receiver further comprises a decoder for decodingthe repetition decoded signal.
 2. The receiver of claim 1, wherein therepetition decoder operates on the lower layer.
 3. The receiver of claim1, wherein the repetition decoded signal represents an averagelog-likelihood ratio (LLR) for every J received signal points of the atleast one demodulated signal, where J>1.
 4. The receiver of claim 1,wherein the repetition decoded signal represents an average of every Jreceived signal points of the at least one demodulated signal, whereJ>1.
 5. The receiver of claim 1, wherein the repetition decoder furthercomprises: a number of averaging elements, each averaging elementaveraging soft input data derived from the at least one demodulatedsignal over a different respective alignment and providing a respectiveaveraged signal; a comparator for determining which averaged signalrepresents a better alignment as compared to the remaining averagedsignals; and a selector for providing the averaged signal determined torepresent the better alignment.
 6. The receiver of claim 5, wherein thesoft input data is a function of log-likelihood ratio (LLR) valuesassociated with the at least one demodulated signal.
 7. A receivercomprising: a demodulator for demodulating a multi-level received signalto provide K demodulated signals, where K>1; and a repetition decoderfor removing duplicated data from at least one of the K demodulatedsignals; wherein the demodulator has a number of operating modes,wherein at least two of the modes are a hierarchical mode and a layeredmode; and wherein the repetition decoder provides a repetition decodedsignal and wherein the receiver further comprises a decoder for decodingthe repetition decoded signal.
 8. The receiver of claim 7, wherein themulti-level received signal is a hierarchically modulated signalincluding at least an upper layer and a lower layer.
 9. The receiver ofclaim 8, wherein the repetition decoder operates on the lower layer. 10.The receiver of claim 7, wherein the multi-level received signal is alayered modulated signal including at least an upper layer and a lowerlayer.
 11. The receiver of claim 10, wherein the repetition decoderoperates on the lower layer.
 12. The receiver of claim 7, wherein therepetition decoded signal represents an average log-likelihood ratio(LLR) for every J received signal points of the at least one demodulatedsignal, where J>1.
 13. The receiver of claim 7, wherein the repetitiondecoded signal represents an average of every J received signal pointsof the at least one demodulated signal, where J>1.
 14. The receiver ofclaim 7, wherein the repetition decoder further comprises: a number ofaveraging elements, each averaging element averaging soft input dataderived from the at least one demodulated signal over a differentrespective alignment and providing a respective averaged signal; acomparator for determining which averaged signal represents a betteralignment as compared to the remaining averaged signals; and a selectorfor providing the averaged signal determined to represent the betteralignment.
 15. The receiver of claim 14, wherein the soft input data isa function of log-likelihood ratio (LLR) values associated with the atleast one demodulated signal.
 16. A receiver comprising: a demodulatorfor demodulating a multi-level received signal to provide K demodulatedsignals, where K>1; and a repetition decoder for removing duplicateddata from at least one of the K demodulated signals; wherein therepetition decoder further comprises a number of averaging elements,each averaging element averaging soft input data derived from the atleast one demodulated signal over a different respective alignment andproviding a respective averaged signal; a comparator for determiningwhich averaged signal represents a better alignment as compared to theremaining averaged signals; and a selector for providing the averagedsignal determined to represent the better alignment.
 17. The receiver ofclaim 16, wherein the soft input data is a function of log-likelihoodratio (LLR) values associated with the at least one demodulated signal.18. A method for use in a receiving apparatus, the method comprising:using the receiving apparatus to perform the steps of: demodulating amulti-level received signal to provide K demodulated signals, where K>1;and removing duplicated data from at least one of the K demodulatedsignals; and wherein the multi-level received signal is a layeredmodulated signal including at least an upper layer and a lower layer;and wherein the removing step includes the step of providing arepetition decoded signal and the method further comprises the step ofdecoding the repetition decoded signal.
 19. The method of claim 18,wherein the repetition decoder operates on the lower layer.
 20. Themethod of claim 18, wherein the repetition decoded signal represents anaverage log-likelihood ratio (LLR) for every J received signal points ofthe at least one demodulated signal, where J>1.
 21. The method of claim18, wherein the repetition decoded signal represents an average of everyJ received signal points of the at least one demodulated signal, whereJ>1.
 22. The method of claim 18, wherein the removing step comprises:averaging soft input data derived from the at least one demodulatedsignal over a number of different alignments and providing a respectiveaveraged signal associated with each alignment; determining whichaveraged signal represents a better alignment as compared to theremaining averaged signals; and providing that averaged signaldetermined to represent the better alignment.
 23. The method of claim22, wherein the soft input data is a function of log-likelihood ratio(LLR) values associated with the at least one demodulated signal.
 24. Amethod for use in a receiving apparatus, the method comprising: usingthe receiving apparatus to perform the steps of: demodulating amulti-level received signal to provide K demodulated signals, where K>1;and removing duplicated data from at least one of the K demodulatedsignals; wherein the demodulating step includes the steps of: selectingone of at least two demodulation modes; and performing the demodulationin accordance with the selected mode; and wherein the at least twodemodulation modes is a hierarchical demodulation mode and a layereddemodulation mode.
 25. The method of claim 24, wherein the multi-levelreceived signal is a hierarchically modulated signal including at leastan upper layer and a lower layer.
 26. The method of claim 25, whereinthe repetition decoder operates on the lower layer.
 27. The method ofclaim 24, wherein the multi-level received signal is a layered modulatedsignal including at least an upper layer and a lower layer.
 28. Themethod of claim 27, wherein the repetition decoder operates on the lowerlayer.
 29. The method of claim 24, wherein the removing step includesthe step of providing a repetition decoded signal and the method furthercomprises the step of decoding the repetition decoded signal.
 30. Themethod of claim 29, wherein the repetition decoded signal represents anaverage log-likelihood ratio (LLR) for every J received signal points ofthe at least one demodulated signal, where J>1.
 31. The method of claim29, wherein the repetition decoded signal represents an average of everyJ received signal points of the at least one demodulated signal, whereJ>1.
 32. The method of claim 24, wherein the removing step comprises:averaging soft input data derived from the at least one demodulatedsignal over a number of different alignments and providing a respectiveaveraged signal associated with each alignment; determining whichaveraged signal represents a better alignment as compared to theremaining averaged signals; and providing that averaged signaldetermined to represent the better alignment.
 33. The method of claim32, wherein the soft input data is a function of log-likelihood ratio(LLR) values associated with the at least one demodulated signal.
 34. Amethod for use in a receiving apparatus, the method comprising: usingthe receiving apparatus to perform the steps of: demodulating amulti-level received signal to provide K demodulated signals, where K>1;and removing duplicated data from at least one of the K demodulatedsignals; and wherein the removing step comprises: averaging soft inputdata derived from the at least one demodulated signal over a number ofdifferent alignments and providing a respective averaged signalassociated with each alignment; determining which averaged signalrepresents a better alignment as compared to the remaining averagedsignals; and providing that averaged signal determined to represent thebetter alignment.
 35. The method of claim 34, wherein the soft inputdata is a function of log-likelihood ratio (LLR) values associated withthe at least one demodulated signal.